155/80R13 vs 175/70R13: Tyre Size Comparison, Diameter Difference & Speedometer Effect

Comparing 155/80R13 with 175/70R13 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 175/70R13 is the shorter tyre: its diameter is 575.2 mm against 578.2 mm, -3.0 mm (-0.5%) smaller. The width changes by +20 mm (155 mm to 175 mm) and the sidewall by -1.5 mm. This page puts both sizes side by side, works out the diameter difference in millimetres and percent, shows the speedometer error in both directions at 30, 50 and 70 mph, and explains what the change means for ride, grip and clearance — so you can judge the swap with the actual figures in front of you.

The short version: a -0.5% diameter difference is inside the commonly used plus-or-minus 3% guideline, which is the usual yardstick for keeping speedometer error small. But diameter is only the first check. The two sizes also differ in width by 20 mm and in rim size (13 inches against 13 inches), so a swap means different wheels as well unless the rims already match. Read the whole comparison before deciding — the clearance and load-index sections matter as much as the headline percentage.

This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.

155/80R13 vs 175/70R13 side by side

Measurement 155/80R13 175/70R13 Difference
Overall diameter 578.2 mm (22.8 in) 575.2 mm (22.6 in) -3.0 mm (-0.5%)
Sidewall height 124.0 mm 122.5 mm -1.5 mm
Circumference 1816.5 mm 1807.0 mm -9.5 mm
Revolutions per mile 886.0 890.6 +4.6
Section width 155 mm 175 mm +20 mm
Rim diameter 13 in 13 in +0 in

Diameter difference between 155/80R13 and 175/70R13: -3.0 mm (-0.5%)

A -0.5% diameter change is small enough to sit inside the commonly used plus-or-minus 3% guideline, so the speedometer error it introduces stays modest. The circumference changes by -9.5 mm per revolution, and the revs per mile change by +4.6, which is the same story told from the car's point of view: the instruments count revolutions, so fewer revs per mile means the car travels further per revolution than the instruments assume. That drift also affects the odometer, so recorded mileage moves by the same percentage over time.

Speedometer error: 155/80R13 to 175/70R13 and back

Going from 155/80R13 to 175/70R13, the diameter grows by -0.5%, so the true speed is the indicated speed multiplied by 0.995. At 30 mph on the dial the car is really doing 29.8 mph; at 50 mph indicated it is 49.7 mph; at 70 mph indicated it is 69.6 mph. The speedometer therefore reads high after the change, which matters most at motorway speed, where even a small percentage is a real difference in miles per hour. Going the other way, from 175/70R13 back to 155/80R13, the error reverses exactly: the ratio becomes 1.005, so 70 mph indicated is really 70.4 mph.

Indicated speed Actual speed fitting 175/70R13 (from 155/80R13) Actual speed fitting 155/80R13 (from 175/70R13)
30 mph 29.8 mph 30.2 mph
50 mph 49.7 mph 50.3 mph
70 mph 69.6 mph 70.4 mph

Sidewall height and ride comfort: 155/80R13 vs 175/70R13

For 155/80r13 vs 175/70r13, the point is this: Sidewall height moves by -1.5 mm between these two sizes (124.0 mm to 122.5 mm), and that is enough to feel. A taller sidewall flexes more, which softens sharp impacts and gives the tyre more give over potholes; a shorter sidewall flexes less, which sharpens the steering response and leaves the rim closer to the road surface on a hard hit. Which of those you get depends on the direction of the change — here the sidewall shrinks — and on the aspect ratio shift from 80% to 70%.

Width, grip and fuel use: 155/80R13 vs 175/70R13

Width changes by +20 mm, from 155 mm to 175 mm. A wider tyre puts a broader contact patch on the road, which generally helps dry grip and braking, but it can also increase road noise and rolling resistance, and it needs more clearance around the suspension and arches. Fuel use moves with rolling resistance, so a wider tyre can cost a small amount of fuel over time — the effect is real but modest for a change of this size, and it is not something this page can put a precise number on without knowing the exact tyre models involved. That is the point this page works through for 155/80r13 vs 175/70r13.

Revolutions per mile and gearing: 155/80R13 vs 175/70R13

The revs-per-mile figures (886.0 for 155/80R13, 890.6 for 175/70R13) describe the gearing effect. 175/70R13 turns +4.6 fewer times per mile, so at any given road speed the engine turns slightly slower with 175/70R13 fitted — the gearing is effectively longer. That can make cruising a touch more relaxed and can trim fuel use slightly, but it also means slightly less acceleration from the same throttle opening, because each gear is effectively taller. The change is 0.5% either way, so the effect on everyday driving is subtle rather than transformative.

Will 175/70R13 clear after 155/80R13? What to check before fitting

Do not skip the physical check. The diameter difference is -0.5% and the width difference is +20 mm, and both of those affect whether 175/70R13 fits where 155/80R13 did. Check the gap between the tyre and the arch, the gap to the suspension arms and struts, and the clearance at full steering lock in both directions. Repeat the check with weight in the car, because suspension travel changes the geometry. If the tyre touches anything at any point in that check, it does not fit, whatever the diameter percentage says. The load index and speed rating need confirming against the placard too, and the rim width must suit a 175 mm tyre.

Which size suits which priority: 155/80R13 or 175/70R13

On this page, 155/80r13 vs 175/70r13 is the case in point: Choose on the basis of what matters to you, not on the headline alone. If ride comfort matters most, the sidewall change of -1.5 mm is the figure to weigh. If grip matters most, the width change of +20 mm is the one to weigh. If keeping the instruments accurate matters most, the diameter change of -0.5% is the one to weigh — and if it is outside the plus-or-minus 3% guideline, ask about recalibration. And if the answer to the clearance check is uncertain, that outranks all three: a tyre that rubs is not a viable option at any percentage.

Related 155/80R13 vs 175/70R13 comparisons and tools

Frequently asked questions

What is the diameter difference between 155/80R13 and 175/70R13?

175/70R13 is -3.0 mm (-0.5%) smaller in diameter than 155/80R13: 575.2 mm against 578.2 mm. That is inside the commonly used plus-or-minus 3% guideline for keeping speedometer error small.

How much will my speedometer be out if I fit 175/70R13 instead of 155/80R13?

The error follows the diameter ratio, -0.5%. At an indicated 30 mph the true speed would be 29.8 mph, at 50 mph indicated it would be 49.7 mph, and at 70 mph indicated it would be 69.6 mph. The full table in both directions is in the speedometer section above.

Is 175/70R13 wider than 155/80R13, and does that matter?

Yes — 175/70R13 is 175 mm wide against 155 mm for 155/80R13, a difference of +20 mm. A wider tyre generally gives more dry grip and can increase rolling resistance and road noise slightly. Width also affects clearance, so check the arches and suspension at full lock.

Will 175/70R13 fit my car if 155/80R13 fits?

Not necessarily. 175/70R13 is shorter by 3.0 mm and 20 mm wider, and it needs a 13-inch rim. Check the wheel arches, suspension and steering lock at full lock in both directions, with the car loaded, and confirm the load index and speed rating against your door-jamb placard. A tyre professional can confirm fitment on your vehicle.

Which size is better, 155/80R13 or 175/70R13?

Neither is better in general — it depends on what you want. 175/70R13 has a -1.5 mm sidewall difference, a +20 mm width difference and a -0.5% diameter difference, so the trade-offs are comfort, grip and instrument accuracy respectively. If the diameter is within the plus-or-minus 3% guideline and the clearance check passes, the choice is a matter of preference; if not, resolve those two points first.